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Now looking at definitions starting with letter "h"

HDCD : High Definition-Compatible CD. A trademark dithering process by Pacific Microsonics. The "HDCD process effectively cancels the additive distortions and simultaneously provides additional data to reduce the subtractive distortions" and is compatible with existing consumer digital playback equipment, claiming that there is a clear improvement in the fidelity of the conventional CD. The process works by converting an analog signal into a digital signal with a word length of "longer than 16 bits" and at a sampling frequency of "greater than 100kHz." These data can then be encoded into the standard CD format, or used with 20- or 24-bit recording/editing hardware/software. When used with an HDCD decoder, the reconstructed signal is output at the appropriate > 16-bit, > 44.1kHz format."

HDTV : High Definition TeleVision. A term designating any television system using many more than the standard number of lines per frame specified in the NTSC, PAL, or SECAM systems. Experimental HDTV systems have been developed to provide high-resolution computer animation for motion pictures, flight simulators, etc., but are unlikely to be used for broadcast any time soon due to their inherent incompatibility with existing broadcast standards. The HDTV standard includes 5.1 audio, using AC-3">AC-3 encoding."

head : (1) On a tape recorder, an electro-magnetic transducer that (i) converts electrical energy in the signal into a magnetic field that induces magnetization in the tape, or (ii) produces an electrical signal in response to the varying remanent magnetism stored along a passing length of tape. See erase head, playback head, record head, sync head. (2) In general, the transducing mechanism used in recording or playing back signals on various media, e.g., the cutting head of a record mastering lathe, the optical head of a motion picture projector, etc.

head gap : See gap.

head losses : Limitations in the frequency response of the signal a tape head can transfer to or read from tape due to its inherent design or construction.

head shield : A metal shield installed around as much of the playback head as is possible, in order to minimize distortion due tokeeping EMI from being picked up.

head stack : The assembly of tape heads in a magnetic recorder. The head stack normally consists of an erase head, a record head, and a playback head. Also called a head block.

Header essentially metadata that describes what is contained in the essence, packet, frame, or file remainder that follows, Typically, it is the part of a packet or frame that indicated the start of the data essence or payload; also, a preamble. Headers usually contain metadata such as addressing and error detection information.

headphone box : See cue box.

headphone mix : See cue mix.

headroom : The amount of additional signal above the nominal input level that can be sent into a module before clipping distortion occurs. On a digital tape, input levels are set very low, -15VU to -12VU, to allow adequate headroom for occasional input peaks that might exceed -12VU. See dynamic headroom, dynamic range, overs.

heads-out heads out: A tape recording which has been rewound and is ready to play. It is generally considered best for long-term storage to leave recordings tails-outtails out for minimum print-through.

helical scan : A type of videotape, data, or audio recorder in which the tape is wrapped around a large rotating drum, on which the actual record and playback heads are mounted. Since the heads rotate quickly and write parallel tracks at a very small angle with respect to the tape path, the signal written on the tape is may times the actual length of the tape itself. Thus, helical scan recording offers very high resolution at low tape speeds. Almost all consumer and professional videotape formats employ the helical scan principle, largely replacing the quadruplex recorder.

Helmholz resonator : A structure used in loudspeaker systems which is designed to resonate at a particular frequency. Because of the particular design of the resonator, the sound at the tuned frequency is dampened, and two bands, one each of higher and lower frequency, are produced, extending the bass response of the loudspeaker.

Henry : (1) See Jecklin disk. (2) A measurement for inductance.

Hertz (Hz) unit of measurement for frequency, often written as Hz, or kHz (kilohertz).

heterodyne : To mix two frequencies together producing the sum and difference of the two input frequencies; any information contained on either original frequency is continued in the sum and difference frequencies. Heterodynes are used as the basic designmodel for all AM, FM, amateur radio, CB, TV, radar, and satellite systems. See amplitude modulation.

HFS : Hierarchical File System. A Mac-specific logical file format for CDs. CDs written in HFS cannot be read on PCs. Compare with ISO 9660.

hi-fi video sound : The result of encoding the stereo soundtracks input to hi-fi type VHS or Beta format videotape recorders on an frequency modulated carrier wave. This information is recorded along with picture data via the video record heads. Reproduction of hi-fi sound approaches digital quality audio.

high band : A type of video system in which the picture information is encoded on a much higher carrier frequency than early color video systems; the broadcast standard currently in use.

high-fidelity : Refers to the reproduction of sound with little or no distortion. At least 15kHz of audio bandwidth is required for stereo high-fidelity.

high-frequency compression : See HX/HX pro.

high-output low-noise (HOLN) : A type of magnetic recording tape with very high sensitivity to applied magnetic fields, and with a very high S/N ratio, commonly used in professional audio applications.

highpass filter : A filter that attenuates the frequencies below its rolloff frequency.

HiPPI : High-Performance Parallel Interface): As the guys a CERN say, its not just for supercomputers anymore. Also known as GSN, or Gigabyte System network, HiPPI is one of the original high-speed LAN technologies and interoperates with Ethernet, fibre channel and ATM. It is an ANSI standard for a full-duplex, low-latency, point-to-point interconnect providing 100 to 200 Mbytes/second over a 50 twisted-pair copper PHY with a maximum length of 25 meters. A serial version uses a glass-fiber PHY at the same speed; future versions will scale up to 6.4 Gbits/second.

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